Conventionally, in a train, as devices for detecting vehicle speed, speed generators are respectively attached to an armature shaft of an electric motor and an axle of a driving wheel rotated by power received from the electric motor via this armature shaft (Patent Document 1).
This is because not only the train speed is detected, but also whether a power transmission system from the electric motor to the wheel is in an abnormal state or not is detected by a comparison between the output results of these speed generators.